Abstract

Ecological connectivity is vital for the dispersal, colonization, and persistence of species within habitats. Anthropogenic disturbances to the landscape fragment connectivity, resulting in isolated populations of species. Culverted road crossings are barriers that restrict the movement of both species and resources along a stream’s length. In anticipation of the future removal of culverts from four first order tributaries of the Little First Broad River, assessments were undertaken to determine the specific impacts culverts have on ecological and biological connectivity. Two sampling methods, baited crayfish traps and single-pass backpack electrofishing, were used to capture fish and crayfish species. Fish species richness was determined via a Before-After-Control-Impact (BACI) design, in which the number of species collected above the culvert at each study site was subtracted from the number below. In-stream movement of crayfish was quantified through a mark and recapture study. Recapture data was analyzed through the Passage Index (PI) equation, which calculated differences in movements between culverted and non-culverted stream sections. Under the BACI design, fish species richness above the culverts was shown to be significantly lower than below (p-value 0.002). PI values of -0.91, -0.55, and -1.0 indicated that while crayfish moved through all sections of the study streams, they were more likely to pass through non-culverted reaches than culverted ones. Comparison of the two sampling methods showed electrofishing to be a far superior estimator of crayfish population numbers than baited traps. The overall results of this study reveal that culverts are playing a role in limiting the distribution and movement of fish and crayfish populations. Limitations to dispersal threaten aquatic biodiversity by fragmenting and isolating populations. Following the future removal of the four culverts, a similar post-assessment study is scheduled. A comparative analysis of pre- and post-removal data will help fully articulate the impacts culverts have on aquatic ecosystems.

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